Co-reporter:Yi Zhou, Feilong Yu, Hua Deng, Yajiang Huang, Guangxian Li, and Qiang Fu
The Journal of Physical Chemistry B June 29, 2017 Volume 121(Issue 25) pp:6257-6257
Publication Date(Web):June 7, 2017
DOI:10.1021/acs.jpcb.7b03374
The morphology evolution under shear during different processing is indeed an important issue regarding the phase morphology control as well as final physical properties of immiscible polymer blends. High-speed thin wall injection molding (HSTWIM) has recently been demonstrated as an effective method to prepare alternating multilayered structure. To understand the formation mechanism better and explore possible phase morphology for different blends under HSTWIM, the relationship between the morphology evolution of polymer blends based on polypropylene (PP) under HSTWIM and some intrinsic properties of polymer blends, including viscosity ratio, interfacial tension, and melt elasticity, is systematically investigated in this study. Blends based on PP containing polyethylene (PE), ethylene vinyl alcohol copolymer (EVOH), and polylactic acid (PLA) are used as examples. Compatibilizer has also been added into respective blends to alter their interfacial interaction. It is demonstrated that dispersed phase can be deformed into a layered-like structure if interfacial tension, viscosity ratio, and melt elasticity are relatively small. While some of these values are relatively large, these dispersed droplets are not easily deformed under HSTWIM, forming ellipsoidal or fiber-like structure. The addition of a moderate amount of compatibilizer into these blends is shown to be able to reduce interfacial tension and the size of dispersed phase, thus, allowing more deformation on the dispersed phase. Such a study could provide some guidelines on phase morphology control of immiscible polymer blends under shear during various processing methods.
Co-reporter:Hongju Zhou, Hua Deng, Li Zhang, and Qiang Fu
ACS Applied Materials & Interfaces August 30, 2017 Volume 9(Issue 34) pp:29071-29071
Publication Date(Web):August 9, 2017
DOI:10.1021/acsami.7b07947
The low efficiency of thermal conductive filler is an unresolved issue in the area of thermal conductive polymer composites. Although it is known that minimizing phonon or electron interfacial scattering is the key for achieving high thermal conductivity, the enhancement is generally limited by preparation methods that can yield the ideal morphology and interfaces. Herein, low temperature expandable graphite (LTEG) is added into a commercial impact modifier (Elvaloy4170), which is then coated onto poly(butylene terephthalate) (PBT) particles with various sizes at millimeter scale between their melting temperatures. Thus, macroscopic segregated filler networks with several considerations are constructed: high LTEG loading leads to a short distance between fillers and a robust filler network; continuous Elvaloy-LTEG phase leads to a continuous filler network; and good interaction among filler and matrix leads to good interfacial interaction. More importantly, the rather large size of PBT particles provides the filler networks with low specific interfacial area, which minimizes the interfacial scattering of phonons or electrons. Relative to homogeneous composites with an identical composition, the thermal conductivity is enhanced from 6.2 to 17.8 W/mK. Such an enhancement span is the highest compared with results reported in the literature. Due to possible “shortcut” behavior, much higher effectiveness can be achieved for the current system than found in literature results when the Elvaloy-LTEG phase is considered as filler, with the effectiveness even exceeding the upper limit of theoretical calculation for highly loaded Elvaloy-LTEG phase with relatively large PBT particle sizes. This could provide some guidelines for the fabrication of highly thermal conductive polymer composites as well as multifunctional polymer composites.Keywords: electrical conductivity; EMI shielding ability; polymer composites; segregated structure; thermal conductivity;
Co-reporter:Wenjing Ji, Hua Deng, Qiang Fu
Composites Science and Technology 2017 Volume 151(Volume 151) pp:
Publication Date(Web):20 October 2017
DOI:10.1016/j.compscitech.2017.07.022
High dielectric constant filler is often used to improve the dielectric properties of polymer. Most studies are focused on the uniform filler dispersion and interface between filler and polymer. Herein, multi-layered films containing BaTiO3 and multi-wall carbon nanotubes (MWCNTs) as fillers, with different filler distributions were designed and prepared, including alternating distribution of layers with/without filler; core-shell distribution with filler concentrated at core or shell; and uniform distribution. The overall filler content in these films was kept constant. These films have almost the same dielectric loss. Interestingly, it was noted that the largest dielectric constant is achieved for sample with filler concentrated at the shell (around 50% higher than the rest at low frequency). Interfacial polarization and filler localization are thought to play important role. However, classic Series model does not take these issues into account. To understand this, a modified Series model was proposed to calculate the dielectric constant of multi-layered films by considering these issues. Such equation is much more accurate at describing experimental results from current study as well as some published literature than classic Series model. Our work demonstrates the importance of hierarchical structure in polymer composites for dielectric property and heterogeneous distribution of filler could be much better than uniform distribution.
Co-reporter:Xiaoyu Li, Hua Deng, Qin Zhang, Feng Chen and Qiang Fu
RSC Advances 2016 vol. 6(Issue 30) pp:24843-24852
Publication Date(Web):25 Feb 2016
DOI:10.1039/C5RA28118K
The dynamic percolation behavior of conductive fillers in conductive polymer composites (CPCs) has drawn wide interest due to its crucial influence on the final properties. It is thought that the viscosity of the neat polymer, filler–polymer interaction and entanglement in the filler network are crucial issues. Meanwhile, the structure and related characteristics of the filler is an important parameter for determining filler properties and various functionalities. However, their influence on the filler dynamic self-assembly process in a polymer matrix has been barely investigated. Herein, three types of carbon black (CB) with different dibutyl phthalate (DBP) absorption have been used to study the electrical percolation behavior in thermoplastic polyurethane with methods including in situ electrical measurement during isothermal annealing, scanning electron microscopy (SEM), and rheological study as well as theoretical analysis. It is observed that a higher DBP value leads to a lower percolation threshold. During dynamic percolation, the activation energy increases almost linearly with DBP absorption. It is thought that the more stable pre-formed conductive networks for CB with more DBP are responsible. Thus, the driving force for the self-assembly process is lower for CB with more DBP. This study provides new insight for the dynamic self-assembly process of a functional filler in a polymer matrix.
Co-reporter:Yi Zhou, Hua Deng, Feilong Yu, Hongwei Bai, Qin Zhang, Feng Chen, Ke Wang, Qiang Fu
Polymer 2016 Volume 99() pp:49-58
Publication Date(Web):2 September 2016
DOI:10.1016/j.polymer.2016.06.013
•The processing condition induced changes in flow field, temperature field, viscosity and shear time.•The changes as above largely influence the confinement of melt during processing, thus, their final phase morphology.•The moderate injection condition and thin mold favors the formation of alternating multi-layer structure.•The confinement of flow plays a key role on formation of alternating multi-layer structure.Polymeric materials with alternating multi-layer structure have gained much attention in the field of biomimic, where many methods were used to prepare materials with such structure for various functionalities. A simple method based on high speed thin-wall injection molding (HSTWIM) has been proposed in our previous studies for the easy fabrication of multi-layer functional polymeric materials. Herein, the effect of various injection processing parameters: injection distance, injection speed, mold temperature and mold thickness on the phase morphology and molecular orientation is studied. The processing condition induced changes in flow field, temperature field, viscosity and shear time are thought to largely influence the confinement of melt during processing, thus, their final phase morphology. It is observed that moderate injection distance, moderate injection speed, moderate mold temperature and thin mold favors the formation of such alternating multi-layer structure. Such study could provide guidelines for the fabrication of functional multi-layered structure through HSTWIM as well as control of phase morphology through confined flow.
Co-reporter:Hongju Zhou, Hua Deng, Li Zhang, Zhiqiang Wu, Sha Deng, Weixing Yang, Qin Zhang, Feng Chen, Qiang Fu
Composites Part A: Applied Science and Manufacturing 2016 82() pp: 20-33
Publication Date(Web):March 2016
DOI:10.1016/j.compositesa.2015.11.030
The distribution of functional filler is known to have significant influence on various functionalities, yet, not been systematically investigated. Herein, we use a blends system based on PA12/PA6 containing SiC and low-temperature expandable graphite (LTEG) to study it. The effect of filler distribution in such blends on various functionalities including: thermal conductivity, electrical conductivity, and electromagnetic interference (EMI) shielding ability, has been systematically studied. Further study on altering filler distribution with polished PA6-LTEG and PA6-LTEG in different sizes reveals that, polished particle surface results in reduced electrical and thermal conductivity; and smaller particle size leads to enhanced electrical conductivity, thermal conductivity and EMI shielding ability. Finally, theoretical approach on thermal conductivity demonstrates that the system illustrates very effective contribution in thermal conductivity from large PA6-LTEG “filler” comparing to much smaller traditional fillers. Such study could provide a guideline for the processing of functional polymer composites.
Co-reporter:Feilong Yu, Hua Deng, Hongwei Bai, Qin Zhang, Ke Wang, Feng Chen, and Qiang Fu
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 19) pp:10178
Publication Date(Web):April 27, 2015
DOI:10.1021/acsami.5b00347
Various methods have been devoted to trigger the formation of multilayered structure for wide range of applications. These methods are often complicated with low production efficiency or require complex equipment. Herein, we demonstrate a simple and efficient method for the fabrication of polymeric sheets containing multilayered structure with enhanced barrier property through high speed thin-wall injection molding (HSIM). To achieve this, montmorillonite (MMT) is added into PE first, then blended with PP to fabricate PE-MMT/PP ternary composites. It is demonstrated that alternating multilayer structure could be obtained in the ternary composites because of low interfacial tension and good viscosity match between different polymer components. MMT is selectively dispersed in PE phase with partial exfoliated/partial intercalated microstructure. 2D-WAXD analysis indicates that the clay tactoids in PE-MMT/PP exhibits an uniplanar-axial orientation with their surface parallel to the molded part surface, while the tactoids in binary PE-MMT composites with the same overall MMT contents illustrate less orientation. The enhanced orientation of nanoclay in PE-MMT/PP could be attributed to the confinement of alternating multilayer structure, which prohibits the tumbling and rotation of nanoplatelets. Therefore, the oxygen barrier property of PE-MMT/PP is superior to that of PE-MMT because of increased gas permeation pathway. Comparing with the results obtained for PE based composites in literature, outstanding barrier property performance (45.7% and 58.2% improvement with 1.5 and 2.5 wt % MMT content, respectively) is achieved in current study. Two issues are considered responsible for such improvement: enhanced MMT orientation caused by the confinement in layered structure, and higher local density of MMT in layered structure induced denser assembly. Finally, enhancement in barrier property by confining impermeable filler into alternating multilayer structure through such simple and efficient method could provide a novel route toward high-performance packaging materials and other functional materials require layered structure.Keywords: barrier; clay; high speed thin wall injection molding; multilayered structure; orientation;
Co-reporter:Li Zhang, Hua Deng, Siyao Liu, Qin Zhang, Feng Chen and Qiang Fu
RSC Advances 2015 vol. 5(Issue 128) pp:105592-105599
Publication Date(Web):02 Dec 2015
DOI:10.1039/C5RA22240K
Post-treatment of PEDOT:PSS films to fabricate high performance thermoelectric (TE) materials has been widely studied. The depletion of PSS and tuning the redox level of PEDOT have been considered important. The effective control of these two issues is crucial, yet has not been systematically investigated. Herein, HI and DMSO are used to post-treat PEDOT:PSS films, issues including using these solvents in a step-wise fashion, using solvent or vapour and treatment time are studied. HI is found to have both a physical doping and reducing effect on PEDOT:PSS simultaneously. However, HI solution or vapour could not remove most of the excess PSS to obtain high electrical conductivity. Therefore, DMSO is used to achieve this. Subsequently, HI vapour was used to alter the redox level. Through this method, the power factor reaches as high as 45.02 μW mK−2, which is over 5000 times higher than the as spun film. These films are characterized by different methods, including: AFM, XPS, UV, SEM and Raman spectroscopy. It is concluded that such enhancement in TE properties is caused by two issues: the depleting effect of PSS by DMSO and oxidation level change of PEDOT by HI vapour. The former leads to enhanced electrical conductivity and the latter leads to reduced charge carrier concentration, thus, enhanced Seebeck coefficient. It is thought that such a two-step solvent post-treatment method could offer a novel route to optimize the TE properties of PEDOT:PSS based materials.
Co-reporter:Siyao Liu, Hua Deng, Yun Zhao, Shijie Ren and Qiang Fu
RSC Advances 2015 vol. 5(Issue 3) pp:1910-1917
Publication Date(Web):27 Nov 2014
DOI:10.1039/C4RA09147G
Poly(3,4-ethylenedioxylthiophene):poly(styrene sulfonate) (PEDOT:PSS) has been investigated as a thermoelectric (TE) material extensively. Post-treatment using various solvents has been used to improve its TE performance. Nevertheless, the effects of using mixed co-solvents and post-treatment temperature have hardly been systematically studied. Herein, the TE properties of PEDOT:PSS thin films after solvent post-treatment are investigated. Different ratios of ethylene glycol (EG) and dimethyl sulfoxide (DMSO) as co-solvents and different treatment temperatures are used to optimize the TE properties. It is demonstrated that DMSO post-treatment is more efficient than the co-solvent or EG single solvent at removing insulating PSS from these thin films due to its high dielectric constant. DMSO treated specimens exhibit a power factor as high as 28.95 μW mK−2. Under room temperature post-treatment, PSS is depleted and conformational changes of PEDOT are triggered. This leads to higher electrical conductivity, without an apparent effect on the redox level of PEDOT. Under higher treatment temperature, PEDOT:PSS shows a certain degree of reduced form which leads to a higher Seebeck coefficient. Meanwhile, the electrical conductivity drops and the Seebeck coefficient increases first and then drops with increasing temperature. The reason that the Seebeck coefficient increases is mainly because of the redox level variation under high temperature. With the combination of co-solvent and temperature, the highest power factor of 37.05 μW mK−2 is obtained for PEDOT:PSS post-treated with DMSO at 120 °C. Assuming a thermal conductivity of 0.17 W m K−1, the corresponding ZT of such PEDOT:PSS film is 0.065. This demonstrates that post-treatment is an effective way to optimize the TE properties of PEDOT:PSS. Furthermore, the combined use of solvent and temperature shows the potential of effective tuning of the TE properties of PEDOT:PSS via a more simple and environmentally friendly process.
Co-reporter:Hua Deng, Lin Lin, Mizhi Ji, Shuangmei Zhang, Mingbo Yang, Qiang Fu
Progress in Polymer Science 2014 Volume 39(Issue 4) pp:627-655
Publication Date(Web):April 2014
DOI:10.1016/j.progpolymsci.2013.07.007
Since the emergence of large aspect ratio and multifunctional conductive fillers, such as carbon nanotubes, graphene nanoplates, etc., conductive polymer composites (CPCs) have attracted increasing attention. Although the morphological control of conductive networks in CPCs has been extensively investigated as an important issue for the preparation of high performance CPCs, recent extensive progress has not been systematically addressed in any review. It has been observed that the morphological control of conductive networks during the preparation of CPCs has crucial influence on the electrical properties of these composites. Several methods have been shown to be able to control the network structure, and thus, tune the electrical properties of CPCs, including the use of shear, polymer blends, thermal annealing, mixed filler, latex particle etc. Moreover, many novel and exciting applications have been extensively investigated for CPCs, such as stretchable conductor, electroactive sensors, shape memory materials and thermoelectric materials, etc. Therefore, the morphological control of conductive network in CPCs is reviewed here. Issues regarding morphology characterization methods, morphological control methods, resulted network morphology and electrical properties are discussed. Furthermore, the use of CPCs as electroactive multifunctional materials is also reviewed.
Co-reporter:Hua Deng, Mizhi Ji, Dongxue Yan, Sirui Fu, Lingyan Duan, Mengwei Zhang and Qiang Fu
Journal of Materials Chemistry A 2014 vol. 2(Issue 26) pp:10048-10058
Publication Date(Web):07 Apr 2014
DOI:10.1039/C4TA01073F
The resistivity–strain behavior of conductive polymer composites (CPCs) has gained intense interest due to its importance for various applications. The resistivity of CPCs often increases substantially and linearly under strain. To achieve constant resistivity under strain, a large filler content and special network configuration are often required. And a tunable step-wise resistivity–strain behavior has yet to be reported. Herein, a new method combining polymer blends and pre-stretching is introduced to modify the resistivity–strain behavior of CPCs based on thermoplastic polyurethane (TPU)/polyolefin elastomer (POE) with multi-walled carbon nanotubes (MWCNTs) selectively incorporated in the TPU phase. Depending on the compositions of blends and the intensity of pre-stretching, various interesting resistivity–strain behaviors have been achieved. The resistivity can be either linearly increasing or constant. Interestingly, two-stepwise resistivity–strain behavior has been achieved, with first an increase then a constant value. To understand this unique phenomenon, the phase morphology and conductive network structure are systematically characterized. It is observed that the orientation of MWCNTs is strongly correlated with overall resistivity. Finally, a mechanism involving fibrillization and “slippage” between conductive phases is proposed to explain the resistivity–strain dependency. This study provides guidelines for the preparation of high performance strain sensors as well as stretchable conductors.
Co-reporter:Lingyan Duan, Sirui Fu, Hua Deng, Qin Zhang, Ke Wang, Feng Chen and Qiang Fu
Journal of Materials Chemistry A 2014 vol. 2(Issue 40) pp:17085-17098
Publication Date(Web):15 Aug 2014
DOI:10.1039/C4TA03645J
The use of conductive polymer composites (CPCs) for strain sensing applications has attracted intense interest lately. The stability and sensitivity of resistivity–strain behaviour are thought to be important issues, but systematic investigations are missing. Herein, the resistivity–strain behavior in terms of stability and sensitivity of CPCs based on poly(styrene-butadiene-styrene) (SBS) containing multiwalled carbon nanotubes (MWCNTs) are studied. It is demonstrated that the preparation method has an important influence on the resistivity–strain behavior of these CPCs. Under linear uniaxial strain, the sensitivity increases with decreasing filler content for both composites, showing higher strain sensitivity near the percolation threshold. Moreover, a higher and wider range of sensitivities is obtained for SBS/MWCNT composites from melt mixing. Under dynamic strain, resistivity downward drifting and shoulder peaks are shown for composites from melt mixing, while linear relationships and reversible resistivity in every cycle are observed for composites from solution mixing, showing good electromechanical consistency, stability and durability. From the TEM, rheology, SEM, SAXS, Raman microscopy and analytical modeling studies, the difference in morphology is thought to be responsible for such resistivity–strain behavior. As more disordered and less densely packed conductive networks in melt-mixed CPCs are more easily destroyed under strain, evenly distributed and densely packed networks in solution mixed CPCs are more stable during cyclic stretching. Finally, human knee motions have been detected using these CPCs, demonstrating a potential application of these CPCs as movement sensors.
Co-reporter:Shuangmei Zhang, Hua Deng, Qin Zhang, and Qiang Fu
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 9) pp:6835
Publication Date(Web):April 18, 2014
DOI:10.1021/am500651v
Morphological control of conductive networks involves the construction of segregated or double-percolated conductive networks is often reported to reduce the electrical percolation threshold of conductive polymer composites (CPCs) for better balance among electrical conductivity, mechanical properties, and filler content. Herein, the construction of conductive networks with both segregated and double-percolated characteristics is achieved based on polypropylene (PP)/polyethylene (PE) and multi-wall carbon nanotubes (CNTs). CNTs were firstly dispersed in PE; then PE/CNTs were compounded with PP particles well below the melting temperature of PP. It is observed that the percolation threshold (pc) decreases with increasing PP particle size (size 3.6 mm, pc = 0.08 wt %), which agrees with previous theoretical prediction and experiment in much smaller particle size range. To further study this, the amount of CNTs in PE is varied. It is shown that the degree of PE/CNTs coating on PP particles varies with CNTs as well as PE content in these composites, and have significant influence on the final electrical property. Furthermore, a model combines classical percolation theory and model for segregated network has been proposed to analyze the effect of particle size, degree of coating and thickness of coating on the percolation behavior of these CPCs. In such a model the percolation of CNTs in PE phase as well as PENT phase in the segregated structure can be described. Overall, through such method, a much better balance among mechanical property, conductivity, and filler content is achieved in these CPCs comparing with the results in literature.Keywords: conductive network; conductive polymer composites; electrical percolation; particle size; segregated and double-percolated network;
Co-reporter:Lin Lin, Siyao Liu, Qi Zhang, Xiaoyu Li, Mizhi Ji, Hua Deng, and Qiang Fu
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 12) pp:5815
Publication Date(Web):May 28, 2013
DOI:10.1021/am401402x
The use of conductive polymer composites (CPCs) as strain sensors has been widely investigated and various resistivity-strain sensitivities are desirable for different applications. In this study, the use of mixed carbon fillers and functionalized carbon nanotubes was demonstrated to be vital for preparing thermoplastic polyurethane (TPU)-based strain sensors with tunable sensitivity. To understand the strain sensing behavior, we carried out scanning electron microscopy (SEM), Raman spectroscopy, wide-angle X-ray diffraction (WAXD), mechanical test, and rheology-electrical measurement. Hybrid fillers of multi-walled carbon nanotubes (MWNTs) and carbon black (CB) could reduce the entanglement in conductive network structure, thus increase the resistivity-strain sensitivity. Furthermore, incorporation of additional functionalized MWNTs in the CPCs could enhance the interfacial interaction between nanofillers and TPU, leading to further increase in sensitivity. Through such a simple method, strain sensors could be efficiently fabricated with large strain-sensing capability (strain as large as 200%) and a wide range of strain sensitivity (gauge factor ranging from 5 to 140238). Finally, the exponential revolution of resistive response to strain was fitted with a model based on tunneling theory by Simmons. It was observed that the change in tunneling distance and the number of conductive pathways could be accelerated significantly by adjusting conductive network structure and interfacial interaction. This study provides a guideline for the preparation of high-performance CPC strain sensors with a large range of resistivity-strain sensitivity.Keywords: conductive polymer composite; interfacial interaction; network structure; sensitivity; strain sensor;
Co-reporter:Li Lin;Xiang Gao;Shuangmei Zhang;Emiliano Bilotti;Ton Peijs;Qiang Fu
Polymer International 2013 Volume 62( Issue 1) pp:134-140
Publication Date(Web):
DOI:10.1002/pi.4291
Abstract
Eutectic metal particles and carbon nanotubes are incorporated into a thermoplastic polyurethane matrix through a simple but efficient method, melt compounding, to tune the resistivity–strain behavior of conductive polymer composite (CPC) fibers. Such a combination of conductive fillers is rarely used for CPCs in the literature. To characterize the strain-sensing properties of these fibers, both linear and dynamic strain loadings are carried out. It is noted that a higher metal content in the fibers results in higher strain sensitivity. These strain-sensing results are discussed through a morphological study combined with a model based on the classic tunneling model of Simmons. It is suggested that a high tunneling barrier height is preferred in order to achieve higher strain sensitivity. Copyright © 2012 Society of Chemical Industry
Co-reporter:Feilong Yu, Hua Deng, Qin Zhang, Ke Wang, Chaoliang Zhang, Feng Chen, Qiang Fu
Polymer 2013 Volume 54(Issue 23) pp:6425-6436
Publication Date(Web):1 November 2013
DOI:10.1016/j.polymer.2013.09.047
To prepare composites with anisotropic conductive networks, electrical conductive polymer composites (CPCs) consisting of polypropylene (PP) and carbon nanotubes (CNTs) filled polyethylene (PE) are fabricated through high speed thin-wall injection molding. Morphological study demonstrates that CNTs are localized in PE phase while the alternating multilayer structure with different polymer phases elongated as well as conductive network oriented parallel to flow direction is observed. To form such alternating layered structure, the dispersed phases are firstly deformed into discontinuous layers, and finally further deformed into wide and regular continuous alternating layers. In term of the mechanism behind this, the good viscosity match, low interfacial tension between different polymer components, short relaxation time and high shear rate are thought as important issues. The anisotropic conductive behavior of these CPCs, i.e. conductive in longitudinal (parallel to flow direction) and transverse (perpendicular to flow direction) direction but non-conductive in thickness direction, is contributed by the insulating PP layer which cuts off the conductive networks in the core layer. More importantly, much better electromagnetic interference (EMI) shielding ability is obtained for these CPCs with alternating multilayer conductive networks comparing with the same polymer blends with isotropic conductive networks, despite of the fact that much lower resistivity is obtained for the later. This indicates great potential of these anisotropic CPCs for electronic applications. Moreover, this study has shed some light on the potential use of such alternating multi-layered structure to prepare a range of multi-functional materials.
Co-reporter:Kun Jiang;Feilong Yu;Hongwei Bai;Jian Gao;Qin Zhang ;Qiang Fu
Journal of Applied Polymer Science 2012 Volume 124( Issue 6) pp:4452-4456
Publication Date(Web):
DOI:10.1002/app.35451
Abstract
The formation of multilayer structures in the high-speed thin wall injection-molded samples of high-density polyethylene/isotactic polypropylene blends is reported. Based on the morphology development in injection runner and mold, a possible formation mechanism of multilayer structure was proposed in this study. Injection molding could be used as a simple and an effective method for the fabrication of multifunctional multilayer structure. This work is interesting and important for scientific research as well as several potential applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Hongwei Bai;Qin Zhang;Ke Wang;Qiang Fu;Zhijie Zhang;Yongfeng Men
Polymer International 2012 Volume 61( Issue 2) pp:252-258
Publication Date(Web):
DOI:10.1002/pi.3180
Abstract
Annealing is thought to be an effective method to promote chain rearrangement in semicrystalline polymers and improve their physical properties. However, little attention has been paid to the annealing of flow-oriented semicrystalline polymers despite its importance in polymer processing. In this work, the microstructural evolution of injection-moulded polypropylene with an oriented shish-kebab structure upon annealing has been explored with differential scanning calorimetry, small-angle X-ray scattering and scanning electron microscopy, Fourier transform infrared spectroscopy and dynamic mechanical analysis. The results show that annealing gives rise to a chain rearrangement in both the crystalline and amorphous phases. Accompanied by the growth and perfecting of the kebabs, relaxation of the initially oriented chains in the amorphous phase is observed. Then, the relationship between the structure and the resulting mechanical properties is established. Copyright © 2011 Society of Chemical Industry
Co-reporter:Fang Mai;Chengjuan Zhou;Meijun Yao;Qiang Fu
Polymer International 2012 Volume 61( Issue 9) pp:1400-1410
Publication Date(Web):
DOI:10.1002/pi.4222
Abstract
To realize the full potential of carbon nanotubes (CNTs) in polymer/CNT nanocomposites, many complicated chemical treatments have been developed to modify the CNTs. Nevertheless, the reinforcing efficiency is still not satisfactory in most cases. In this study, a dramatically improved mechanical enhancement is obtained for polyamide 1010/multiwalled carbon nanotube (MWNT) composites simply by exerting high-rate drawing and incorporating a commercially available compatibilizer. For the fibers prepared at high draw ratio, their tensile strength and modulus are improved by 137 and 132%, respectively, through adding only 0.5 wt% MWNTs. In particular, the increase in strength is at a very high level for the case of non-covalent interaction since CNTs could be stretched to failure according to theoretical calculation. It is demonstrated that this reinforcement is mainly attributed to the compatibilizer inducing good dispersion, and the high-rate drawing inducing strong interfacial interaction and orientation of MWNTs. Copyright © 2012 Society of Chemical Industry
Co-reporter:Shuangmei Zhang;Lin Lin;Xiang Gao
Colloid and Polymer Science 2012 Volume 290( Issue 14) pp:1393-1401
Publication Date(Web):2012 September
DOI:10.1007/s00396-012-2661-7
Dynamic percolation in highly oriented conductive networks formed with different carbon nanofillers is investigated during disorientation upon annealing. Conductive networks are constructed by solid-state drawing, subsequent annealing, and using fillers with different dimensions (multiwalled carbon nanotubes (MWCNTs) and carbon black (CB)) in a bicomponent tape. Interestingly, it is observed that a less entangled network work is formed by mixed filler containing CB; consequently, this result in an accelerated dynamic percolation process and reduced activation energy of such process. Three different analytical approaches have been utilized to analyze this interesting behavior. It is concluded that the dynamic percolation process in highly oriented conductive polymer composites filled with MWCNTs can indeed be accelerated by the addition of CB, since less entangled networks are formed in a hybrid filler system compared with MWCNTs alone.
Co-reporter:Hua Deng;Emiliano Bilotti;Rui Zhang;Ke Wang;Qin Zhang;Ton Peijs;Qiang Fu
Journal of Applied Polymer Science 2011 Volume 120( Issue 1) pp:133-140
Publication Date(Web):
DOI:10.1002/app.33140
Abstract
The effect of processing method and condition on the dispersion status of multiwalled carbon nanotubes (MWCNTs), and mechanical properties of the MWCNT/polyamide 6 (PA6) composites are investigated. Different melt processing conditions are used to dilute the master batch produced by melt process or in situ polymerization. Both MWCNTs and carboxyl group functionalized MWCNTs (MWCNTs-COOH) are compounded with PA6 at different loadings (0.1, 0.25, 0.5, and 0.75 wt %) to study the effect of chemical modification of MWCNTs on the mechanical properties of the final composites. It is demonstrated that chemical modification of MWCNTs has a positive effect on the strength of the composites as an increase of 5–10 MPa was observed. More importantly, a near 5 MPa increase in strength and more importantly, a maximum of 138% increase in strain at break were observed for the composites produced by in situ polymerization, indicating a toughening and strengthening effect of CNT on the composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Meijun Yao;Fang Mai;Nanying Ning;Ke Wang ;Qiang Fu
Journal of Applied Polymer Science 2011 Volume 120( Issue 6) pp:3565-3573
Publication Date(Web):
DOI:10.1002/app.33565
Abstract
To extend the application of a carbon dioxide sourced environmental friendly polymer: poly (propylene carbonate) (PPC), a small amount of maleic anhydride (MA) was melt blended to end-cap with PPC to improve its thermal stability and mechanical properties. Thermal and mechanical properties of end-capped PPC were investigated by TGA, GPC, mechanical test, and DMA. TGA and titration results demonstrate that PPC can be easily end-capped with MA through simple melt blending. TGA results show that the thermal degradation temperature of PPC could be improved by around 140°C by adding MA. GPC measurement indicates that the molecular weight of PPC can be maintained after blending with MA, where pure PPC experiences a dramatic degradation in molecular weight during melt process. More importantly, the tensile strength of PPC after blending with MA was found to be nearly eight times higher than that of pure PPC. It has approached the mechanical properties of polyolefin polymers, indicating the possibility of replacing polyolefin polymers with PPC for low temperature applications. The method described here could be used to extend the applications of PPC and fight against the well known global warming problem. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Fang Mai;Dongdong Pan;Xiang Gao;Meijun Yao;Ke Wang;Feng Chen ;Qiang Fu
Polymer International 2011 Volume 60( Issue 11) pp:1646-1654
Publication Date(Web):
DOI:10.1002/pi.3144
Abstract
In this work, polyamide 66 (PA66) and its composites with multiwalled carbon nanotubes (MWNTs) were melt spun into fibers at different draw ratios. PA66 fibers at high draw ratio demonstrate a 40% increase in tensile strength, 66% increase in modulus and a considerable increase in toughness. It is demonstrated that this reinforcement can be mainly attributed to high-draw-ratio-induced good dispersion and orientation of MWNTs, particularly the enhanced interfacial adhesion between MWNT and matrix thanks to interfacial crystallization. Our work provides a simple but efficient method to achieve good dispersion and strong interfacial interaction through melt spinning. Copyright © 2011 Society of Chemical Industry
Co-reporter:Chaoqun Li;Qinna Zhao;Chen Chen;Ke Wang;Qin Zhang;Feng Chen;Qiang Fu
Polymer International 2011 Volume 60( Issue 11) pp:1629-1637
Publication Date(Web):
DOI:10.1002/pi.3141
Abstract
The morphology and properties of multiwalled carbon nanotube modified polypropylene (PP)/ethylene–octene copolymer blends were studied. Polypropylene chains are covalently grafted onto the surface of carbon nanotubes (CNTs) in order to improve their interaction with the polymer matrix. It is observed that functionalization of CNTs improves their dispersion and increases the interfacial bonding between CNTs and polymer matrix. The functionalized CNTs are selectively distributed in the continuous polypropylene phase. The size of the dispersed elastomer phase decreases after the addition of CNTs. Functionalized CNTs act as a nucleating agent and increase the crystallinity of the polypropylene. More importantly, an important increase in impact strength, stiffness and toughness can be achieved through introducing functionalized CNTs. Copyright © 2011 Society of Chemical Industry
Co-reporter:Chaoqun Li;Ke Wang;Qin Zhang;Feng Chen ;Qiang Fu
Journal of Applied Polymer Science 2011 Volume 121( Issue 4) pp:2104-2112
Publication Date(Web):
DOI:10.1002/app.33892
Abstract
In this article, it is demonstrated that simultaneously strengthened and toughened nanocomposites based on polypropylene/EPDM thermoplastic elastomer (TPO) matrix can be achieved through enhanced adhesion between MWNTs and polymer matrix by using PP grafted multiwalled carbon nanotubes (MWNTs). To improve the interface between filler and matrix, MWNTs were treated with acid, or covalently linked to polypropylene. The chemical and morphological transformation of the modified MWNTs, and its effect on the morphology and mechanical properties of the composites are investigated. The strengthening and toughening mechanism is discussed regarding the structural property relationship. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Hongwei Bai, Feng Luo, Tiannan Zhou, Hua Deng, Ke Wang, Qiang Fu
Polymer 2011 Volume 52(Issue 10) pp:2351-2360
Publication Date(Web):4 May 2011
DOI:10.1016/j.polymer.2011.03.017
Large amount of work has been reported on the annealing of polypropylene (PP) and the related changes in mechanical properties. However, the structure–property correlations and the physical origin of annealing induced microstructural evolution are still not very clear. In this work, taking β-form PP (β-PP) as example, the microstructural changes induced by annealing were investigated from macromolecular to crystalline lamellae level with Fourier transform infrared (FTIR) spectroscopy, conventional differential scanning calorimetry (DSC), temperature-modulated DSC (TMDSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA). Besides mobile amorphous fraction (MAF), the role of rigid amorphous fraction (RAF) in toughening PP is particularly taken into consideration. It is shown that annealing increases the chain mobility in MAF and decreases it in RAF. Such an effect is believed to be mainly associated with the formation of looser MAF and more RAF by the microstructural re-arrangement involving conformational ordering of partial amorphous chain segments and a significant interlamellae thickening. A thorough analysis of structure–property relationship through observing plastic deformation behaviors by scanning electron microscope (SEM) and estimating stress transmission between crystalline and amorphous phases, suggests that both MAF and RAF play important role on toughening β-PP. They can promote the initiation of microvoids effectively upon deformation by reducing the stress transmission. As a result, large-scale plastic deformation is triggered. This work is important and provides a new insight into the mechanisms of microstructural evolution and subsequent improvement in impact toughness during annealing.
Co-reporter:Kun Jiang;Fei-long Yu;Run Su;Jing-hui Yang
Chinese Journal of Polymer Science 2011 Volume 29( Issue 4) pp:456-464
Publication Date(Web):2011 July
DOI:10.1007/s10118-011-1049-3
Thin wall samples of high density polyethylene (HDPE) were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Young’s modulus was observed with increasing injection speed. In order to investigate the mechanism behind this decrease, the orientation, molecular weight, molecular weight distribution, melt flow rate, crystallinity and crystal morphology of HDPE were characterized using two-dimensional wide-angle X-ray diffraction (2D-WAXD), gel permeation chromatography (GPC), capillary rheometry and differential scanning calorimetry (DSC), respectively. It is demonstrated that the orientation, molecular weight, molecular weight distribution, melt flow rate and crystallinity have no obvious change with increasing injection speed. Nevertheless, the content of extended chain crystals or large folded chain crystals was found to decrease with increasing injection speed. Therefore, it is concluded that the decrease in tensile properties is mainly contributed by the reduced content of extended chain crystals or large folded chain crystals. This study provides industry with valuable information for the application of high speed injection molding.
Co-reporter:Hongwei Bai, Weiyi Zhang, Hua Deng, Qin Zhang, and Qiang Fu
Macromolecules 2011 Volume 44(Issue 6) pp:1233-1237
Publication Date(Web):February 14, 2011
DOI:10.1021/ma102439t
Co-reporter:Fang Mai, Ke Wang, Meijun Yao, Hua Deng, Feng Chen and Qiang Fu
The Journal of Physical Chemistry B 2010 Volume 114(Issue 33) pp:10693-10702
Publication Date(Web):August 2, 2010
DOI:10.1021/jp1019944
The formation of a shish kebab (SK) structure, where carbon nanotubes (CNTs) serve as shish and polymer lamellae serve as kebab, is particularly interesting and provides a novel way to enhance the polymer−CNT interface. A fine SK structure is achieved through melt spinning. High density polyethylene and pristine CNTs were first compounded in an extruder. The compound was then spun into fibers with different draw ratios with the aid of a capillary rheometer. The crystalline structure and mechanical behavior were characterized by scanning electron microscopy, differential scanning calorimetry, two-dimensional wide-angle X-ray scattering, polarized Raman spectroscopy, and tensile testing. An increase in tensile strength as high as 3 times has been achieved in the fiber. The formation of SKs is considered as the main mechanism responsible for the enhanced interfacial interaction and excellent tensile property.
Co-reporter:Yi Zhou, Yan Zhou, Hua Deng, Qiang Fu
Composites Part A: Applied Science and Manufacturing (May 2017) Volume 96() pp:
Publication Date(Web):May 2017
DOI:10.1016/j.compositesa.2017.02.002
The morphology of conductive network and their interfacial interaction with polymer matrix is thought as the key influential issues for the pressure/strain sensing behavior of conductive polymer composites (CPCs). The surface characteristics and size of these secondary insulating fillers should significantly influence the pressure/strain sensing behavior due to its influence on the morphology of conductive network and interfacial interaction between filler and polymer matrix. Herein, insulating SiO2 with different size and surface characteristics are incorporated into carbon black (CB)/silicon rubber (SR) composites to modify its piezo-resistive behavior. The conductivity of CB/SiO2/SR composites with nanoscale and hydrophobic SiO2 changes by several orders of magnitude, with more linear proportional to applied pressure and better stability under long term cyclic pressure due to better dispersion and stronger interfacial interaction. Through such simple method, high-performance piezo-resistive sensors could be fabricated with reversible piezo-resistivity, large pressure application (pressure below 2500 kPa) and tunable piezo-resistive sensitivity.
Co-reporter:Hua Deng, Lin Lin, Mizhi Ji, Shuangmei Zhang, Mingbo Yang, Qiang Fu
Progress in Polymer Science (April 2014) Volume 39(Issue 4) pp:627-655
Publication Date(Web):1 April 2014
DOI:10.1016/j.progpolymsci.2013.07.007
Since the emergence of large aspect ratio and multifunctional conductive fillers, such as carbon nanotubes, graphene nanoplates, etc., conductive polymer composites (CPCs) have attracted increasing attention. Although the morphological control of conductive networks in CPCs has been extensively investigated as an important issue for the preparation of high performance CPCs, recent extensive progress has not been systematically addressed in any review. It has been observed that the morphological control of conductive networks during the preparation of CPCs has crucial influence on the electrical properties of these composites. Several methods have been shown to be able to control the network structure, and thus, tune the electrical properties of CPCs, including the use of shear, polymer blends, thermal annealing, mixed filler, latex particle etc. Moreover, many novel and exciting applications have been extensively investigated for CPCs, such as stretchable conductor, electroactive sensors, shape memory materials and thermoelectric materials, etc. Therefore, the morphological control of conductive network in CPCs is reviewed here. Issues regarding morphology characterization methods, morphological control methods, resulted network morphology and electrical properties are discussed. Furthermore, the use of CPCs as electroactive multifunctional materials is also reviewed.
Co-reporter:Lingyan Duan, Sirui Fu, Hua Deng, Qin Zhang, Ke Wang, Feng Chen and Qiang Fu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 40) pp:NaN17098-17098
Publication Date(Web):2014/08/15
DOI:10.1039/C4TA03645J
The use of conductive polymer composites (CPCs) for strain sensing applications has attracted intense interest lately. The stability and sensitivity of resistivity–strain behaviour are thought to be important issues, but systematic investigations are missing. Herein, the resistivity–strain behavior in terms of stability and sensitivity of CPCs based on poly(styrene-butadiene-styrene) (SBS) containing multiwalled carbon nanotubes (MWCNTs) are studied. It is demonstrated that the preparation method has an important influence on the resistivity–strain behavior of these CPCs. Under linear uniaxial strain, the sensitivity increases with decreasing filler content for both composites, showing higher strain sensitivity near the percolation threshold. Moreover, a higher and wider range of sensitivities is obtained for SBS/MWCNT composites from melt mixing. Under dynamic strain, resistivity downward drifting and shoulder peaks are shown for composites from melt mixing, while linear relationships and reversible resistivity in every cycle are observed for composites from solution mixing, showing good electromechanical consistency, stability and durability. From the TEM, rheology, SEM, SAXS, Raman microscopy and analytical modeling studies, the difference in morphology is thought to be responsible for such resistivity–strain behavior. As more disordered and less densely packed conductive networks in melt-mixed CPCs are more easily destroyed under strain, evenly distributed and densely packed networks in solution mixed CPCs are more stable during cyclic stretching. Finally, human knee motions have been detected using these CPCs, demonstrating a potential application of these CPCs as movement sensors.
Co-reporter:Hua Deng, Mizhi Ji, Dongxue Yan, Sirui Fu, Lingyan Duan, Mengwei Zhang and Qiang Fu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 26) pp:NaN10058-10058
Publication Date(Web):2014/04/07
DOI:10.1039/C4TA01073F
The resistivity–strain behavior of conductive polymer composites (CPCs) has gained intense interest due to its importance for various applications. The resistivity of CPCs often increases substantially and linearly under strain. To achieve constant resistivity under strain, a large filler content and special network configuration are often required. And a tunable step-wise resistivity–strain behavior has yet to be reported. Herein, a new method combining polymer blends and pre-stretching is introduced to modify the resistivity–strain behavior of CPCs based on thermoplastic polyurethane (TPU)/polyolefin elastomer (POE) with multi-walled carbon nanotubes (MWCNTs) selectively incorporated in the TPU phase. Depending on the compositions of blends and the intensity of pre-stretching, various interesting resistivity–strain behaviors have been achieved. The resistivity can be either linearly increasing or constant. Interestingly, two-stepwise resistivity–strain behavior has been achieved, with first an increase then a constant value. To understand this unique phenomenon, the phase morphology and conductive network structure are systematically characterized. It is observed that the orientation of MWCNTs is strongly correlated with overall resistivity. Finally, a mechanism involving fibrillization and “slippage” between conductive phases is proposed to explain the resistivity–strain dependency. This study provides guidelines for the preparation of high performance strain sensors as well as stretchable conductors.
